Hi Diego, the rules will never contradict each other, nor will the correct answers ever contradict the rules. If you are finding that your possibilities are contradicting the rules, that would be a suggestion that you may have misinterpreted one of the rules or made an error in reasoning, so it would be a good idea to go back and re-read the rules and make sure you notated them correctly. It happens all the time that we might make a mistake in our initial set up, so it's a good idea to go back and check.
